The present application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent application No. 2000-156951 filed on May 26, 2000, the entire content of which is incorporated herein by reference.
The present invention is directed to an electromagnetic valve and in particular to an electromagnetic valve which can switch a flow passage of fluid or which can control flow rate of fluid.
A conventional electromagnetic valve of this kind is disclosed, for example, in Japanese Laid-open Publication No. Hei. 11-2354. This valve is the so-called linear type electromagnetic valve. Namely, the amount of the current supplied to a coil is controlled and thereby the axial position of a spool disposed in a sleeve performing reciprocating motion is controlled continually or without any steps. In this valve, the stepped configuration is processed on an inner circumference of the end of a cylindrical case and a thin portion is formed thereon. A yoke having an outer diameter portion with a diameter substantially the same as the inner diameter of the thin portion and the sleeve is inserted into the thin portion in order. Then, an excess portion of the thin portion which is projected in the axial direction is riveted inward in the diametrical direction and the yoke and the sleeve are secured to the main body of the electromagnetic valve.
Japanese Laid-open Publication No. Hei. 11-118063 also discloses a linear type electromagnetic valve. In this valve, as same as the above mentioned valve, a sleeve having an outer diameter portion with a diameter substantially the same as the inner diameter of a thin portion of the cylindrical case is inserted into the thin portion. Then, an excess portion of the thin portion, which is projected in the axial direction, is riveted inward in the diametrical direction and the sleeve is secured to the main body of the electromagnetic valve.
In the above mentioned valves, the process for forming the stepped configuration having the thin portion on inner circumference of the case is required for riveting the sleeve and so on. Therefore, the manufacturing or processing cost of the valve is increased. Further, the fact that the riveting cannot make the securing portion between the case and the sleeve and so on has a sealing function. Therefore, it is necessary to provide an additional seal number such as a seal ring for preventing the fluid from leaking to the outside of the valve and for preventing the water or dust from entering into the inside of the valve. As a result, the costs of parts and the costs for assembling the valve are increased.
Further, in the electromagnetic valve with the above-mentioned sleeve, the outer diameter of the main body of the valve is generally larger than the outer diameter of the sleeve. Therefore, it is necessary to provide at the and of the sleeve a flange portion whose diameter is substantially the same as the inner diameter of the thin portion. On the other hand, the roughness of the outer circumferential surface of the sleeve on which at least two ports are formed has to be finished by grinding or other methods in order to seal the ports with a member for receiving the sleeve. It is desirable to use an outer circumference centerless method which is cheap for grinding the outer circumferential surface of the sleeve. In order to use such a method, it is necessary that the outer diameter of the outer circumferential surface of the sleeve for grinding is the largest diameter of the sleeve in the axial direction. If the sleeve has a flange portion with a diameter larger than the outer diameter of the outer circumferential surface of the sleeve for grinding, it is not possible to use the outer circumference center-less method. The cost for grinding process is therefore increased. Accordingly, an electromagnetic valve which is cheap and easy to assemble is requested.
It is, therefore, a principal object of the present invention to provide an electromagnetic valve which is cheap and easy to assemble.
In order to attain the foregoing object, the present invention provides an electromagnetic valve which comprises a case having a cylindrical portion, a yoke having a large diameter portion and a small diameter portion, and a sleeve having at least two ports and receiving a valve member therein so as to be able to perform reciprocating motion, wherein the large diameter portion of the yoke is fluid-tightly pressed into the inner circumferential surface of the cylindrical portion of the case and the inner circumferential surface of the sleeve is fluid-tightly pressed onto the outer circumferential surface of the small diameter portion of the yoke.